We have upgraded our Oyster to the Oyster V with screw, went to S&G (Smith & Gosnold) to have it fitted and we are delighted with the system, the fitting & the time S&G spent with us so that we understanded the new system. I have no connection with the firm and didn't know of their existence till they were one of Oyster Tech recommendations. If anyone is thinking of upgrading I would recommend they visit S&G who I believe are exhibitioning at Lincoln Show this weekend.